Train near Eastburn in The Underground (12)
I believe the answer is:
subterranean
'underground' is the definition.
('subterranean' can be a synonym of 'underground')
'train near eastburn' is the wordplay.
'train' indicates anagramming the letters (to train can mean to grow something into a shape).
'near'+'eastburn'='neareastburn'
'neareastburn' with letters rearranged gives 'SUBTERRANEAN'.
'in the' is the link.
(Other definitions for subterranean that I've seen before include "Underground; secret" , "beneath the waves" .)